Facsimile receiver



March 16, 1954 E s GRIMES 2,672,504 1 FACSIMILE RECEIVER Filed March 16, 1951 6 Sheets-Sheet 2 F G 3 S59 60 6| [62 I XI l z FIG.5

SIGNAL AT xx DETECTED DOUBLE CARRIER QUADRUPLE CARRIER COMPONENTS PLUS ENVELOPE PLUS ENVELOPE AT YY L AT YY' 4 AT YY C I l OUTPUT SIGNAL AT 22' d I F -f uousa AT xx e E l NOISE AT YY' NOISE AT 22' g PASS BAND OF l I I FILTER AA as I h I l I 0 2 4 6 8 IO l2 FREQUENCY l N KC IN VEN TOR.

E. S. CRIMES BY I AT ORNEY Nonss VOLTAGE MILLIVOLTS March 16, 1954 GRIMES 2,672,504

FACSIMILE RECEIVER Filed March 16 1951 6 Sheets-Sheet 5 24 F l G. 6

C\ a -a FREQUENCY KC T BASIfGROUND THRESHOLD u Z I Q I m m 0 INVEN TOR.

CURRENT THROUGH PAPER BY E' GRIMES AT RNEY March 16, 1954 E. s. GRIMES 2,672,504

FACSIMILE RECEIVER Filed March 16, 1951 6 Sheets-Sheet 4 I 0 8 '2 E u n: u: 3 U

Fl G. H

(n in U] 2 I Q I m ll] 0 I (n o 25 5o 75 IOO SIGNAL VOLTS IN PER CENT OF BLACK F l6. '2 FIG. '3

m D 65 e0 I D. l l-i- 5 'NPUT DB INVENTOR.

ATTORNEY March 16, 1954 E. S. GRIMES FACSIMILE RECEIVER 6 Sheets-Sheet 5 Filed March 16, 1951 A TORNEY Patented Mar. 16, 1954 sag-ars. Grimes, Rid

I gewood, N. J., assignor to The; Western Union Telegraph Company, New

York, N. Y., a corporation of New York Application March 16, 1951, Serial No. 215,967

9 Claims.

The present invention relates to telegraphic communication by facsimile signals and more particularly to receiving and recording facsimile signals.

When receiving facsimile signals transmitted over a radio channel, interference or noise signals tend to produce background marks on the recording copy sheet during spacing intervals, i. e., intervals during which the received carrier is not modulated with a facsimile signal. These interference or noise signals may emanate from various sources. One such source, which is particularly troublesome when using a frequency modulation channel, sen adjacent voice modulated FM signal. Another source, which is of particular importance in mobile facsimile recorders, is automotive ignition noise.

The presence of background marks on a facsimile copy sheet causes the copy sheet to appear soiled and materially reduces the legibility of the recorded information.

Accordingly, it is an object of the invention to provide facsimile receiving and recording appa' ratus in which the copy sheet will be substantially free of background marks caused by inter ference or noise signals.

More particularly, it is an object of the invention to provide facsimile receiving and recording apparatus having low sensitivity toihterference or noise signals during spacing intervals.-

A further object of the invention is to provide a facsimile receiver and recorder suitable for use on a frequency modulation channel and iii which background marks on the copy sheet re sulting from interference due to voice modulated FM channels are substantially eliminated.

Another object or the invention is to provide a simple and compact facsimile receiver and recorder suitable for use in' a mobile installation and in which copy sheet background marks resulting from igflitioli Or other noise signals are substantially eliminated.

Further objects of the invention will appear from the following description.

According to the invention, these objects are achieved by providing a facsimile receiver and recorder coupled to the output of a radio receiver and comprising a biased facsimile carrier ire-- quency multiplier and a recording amplifier arranged to shorten and straighten the effective recording characteristic of the recording copy sheet. I

The invention will now b described greater detail with reference to the appended drawings in which:

Fig. 1 is a block diagram of a facsimile transmitter station;

Fig. 2 isa block diagram of a facsimile receiver and recorder in accordance with the invention;

Fig. 3 illustrates a carrier frequency doubler and filter in accordance with the invention;

Fig. 4 illustrates a carrier frequency quadrupler and filter in accordance with the invention;

Fig. 5 is a series of curves showing the noise and interference suppression characteristics of thecircuits of Figs. 3 and 4;

Fig. 6 is a series ofcurves illustrating the noise frequency-energy relationship at various points in the circuit of Fig. 3;

Figs. 7 and 8 illustrate recording circuits for facsimile copy sheets; a

Fig. 9 illustrates the current-shade characteristic for a typical recording copy sheet;

Fig. 10 shows the voltage-current characteristic curves for a typical recording copy sheet included in various recording circuits;

Fig. 11 shows voltage-shade characteristic curves for a recording copy sheet; V

Fig. 12 illustrates a carrier frequency doubler provided with a threshold control voltage;

Fig. 13 shows the transmission loss character-; istics of the circuit of Fig. 12 for two values of threshold control voltage; and

Figs. 14 and 15show a facsimile receiver and recorder in accordance with the invention.

Referring now to the drawing and more particularly to Fig. 1, the markings on a copy sheet 2| are scanned by a light beam 22 from lamp 23, the reflected light passing through a small aperture 24 of a diaphragm 25 and onto a phototubezt. The speed of movement of the copy sheet 2| is adjusted relative to the maritings thereon so that the facsimile signal developed across phototube load resistor 27 contains the desired frequency range. For purposes of illustration, a frequency range of from 0 to 2000 cycles will be assumed. It is to be understood, however, that this frequency range, as well as other frequencies and ranges to be specified hereinafter, are given solely for purposes of illustration and are not tobe considered as limiting.

The facsimile signal developed across resistor 2! is applied to D.- C. amplifier and inverter 28, the output of which is applied to a balanced modulator Z9. Amplifier and inverter 28 may comprise, for instance, a single stage triode amplifier. I

'Ihose portions of the facsimile signal applied to modulator 29 which correspond to marks on copy sheet 2! are characterized by maximum voltage. The facsimile signal in modulator 29 is modulated on an oscillation from an oscillator 30. If this oscillation has a frequency of 11,700 cycles, the output of modulator 29 will include frequencies lying within the range 9,700 to 13,700 cycles. A filter 3|, intercoupling modulator 29 and a transfer modulator 32, suppresses all frequencies lying outside this range. The facsimile signal in transfer modulator 32 is modulated on an oscillation of 14,000 cycles from an oscillator 33, the modulated signal being applied to a filter 34 to suppress all modulation components lying outside the range 300 to 4300 cycles. The resultant facsimile signal constitutes a 2300 cycle carrier having a 2000 cycle envelope. This signal is applied to a frequency modulation transmitter 35 and the resultant FM wave is transmitted from an antenna 36.

The double modulation process described produces an undistorted facsimile signal envelope on a carrier having a frequency only slightly higher than the range of facsimile signal frequencies. Other modulation methods tend to produce appreciable amounts of distortion.

Balanced modulator 29 and transfer modulator 32 may be of any conventional type. For instance, transfer modulator 32 may conveniently be realized as a modulator of the type shown in U. S. Patent 2,462,093, issued February 22, 1949, to E. S. Grimes.

In Fig. 2, an FM wave received on an antenna 40 is applied to an FM receiver 4!. The received FM wave may emanate from a transmitter of the type shown in Fig. l or from any other FM transmitter. The demodulated output of receiver 4| is applied to a filter 42. Assuming the frequency ranges of Fig. l, filter 42 should suppress all frequencies lying outside the range of 300 to 4300 cycles.

The output of filter 42, which comprises a 2300 cycle carrier with a 2000 cycle envelope, 1. e., 300 to 4300 cycles, is applied to a frequency doubler 43, the output of which includes a carrier frequency of 4600 cycles having a 2000 cycle envelope, i. e., 2600 to 6600 cycles. The output of doubler 43 is applied to a filter 44 which suppresses frequencies lying outside the 2600 to 6600 cycle range. A threshold control 45 prevents transmission of energy from doubler 43 to filter 44 except when the energy level exceeds a predetermined value.

The output of filter 44 is applied to a recording amplifier 46, the output of which is, in turn, applied to a stylus 41 arranged to scan a copy sheet 48 on a drum 49 driven by a motor 50. The arrangement of Fig. 2 will be described in greater detail hereinafter in connection with Figs. 14 and 15.

During spacing intervals, i. e., intervals during which a blank portion of the copy sheet at the transmitter is being scanned, the FM receiver output should have some predetermined minimum value such as zero. In practice, however, the receiver output during spacing will exceed the desired minimum value because of interference or noise signals modulated on the FM carrier or otherwise present in the receiver. For instance, voice modulated FM signals having the same or an adjacent FM carrier frequency will produce interference signals in the receiver output lying within the voice frequency range. Automotive ignition noise, which is predominantly high frequency in character, will appear 4. at the output of receiver 4| as voice frequency noise signals.

During marking intervals, these interference and noise signals will be modulated on the low frequency facsimile carrier and will tend to vary the shade of the marks produced on copy sheet 48. However, such shade variations are not unduly objectionable. During spacing intervals, on the other hand, the interference and noise signals will tend to cause stylus 41 to record marks, thereby producing the effect of a soiled copy sheet. If these signals are sufiiciently strong, it may become difficult to differentiate between the background and marks.

The carrier frequency doubler and filter illustrated in Fig. 3 serves to suppress a large proportion of the interference and noise signals present in the receiver output during spacing intervals. The carrier frequency doubler, which comprises rectifier elements 55, 5B, 51 and 58 poled as shown in Fig. 3, causes the low frequency facsimile carrier frequency to double, although modulation components in the envelope thereof retain the same absolute spacing from the doubled carrier.

In the example assumed, the instantaneous value e of the voltage at terminals XX is given by the relationship:

K4 (-E cos 21rf t)+ where and K2 and K4 indicate amplitude constants. In this latter equation, the low frequency facsimile carrier of 2300 cycles has been suppressed by being balanced out, and new components have been generated. These new components include a second harmonic of the carrier, indicated by A2=sin 2(21rf2t) where the sin is a function of 2]2 or 4600 cycles, and having the original 2000 cycle envelope. Also included are successive even harmonics each with the original envelope.

A T filter section comprising a first series branch 59 and 60, a second series branch GI and 62 and a shunt branch 63 and 64 intercouples terminals YY' and ZZ'. The filter passes substantially only the second harmonic of the carrier plus or minus the envelope frequencies, so that the wave at terminals 22' is constituted almost entirely by frequencies within the range 2600 to 6600 cycles.

Fig. 4, which illustrates a carrier frequency quadrupler, comprises a first doubler section 65 and a first filter section 66, identical to the doubler and filter section, respectively, of Fig. 3. However, at terminals ZZ' of Fig. 4 there is added a second doubler section 61 similar to section 05 and a filter section '68 tuned to a frequency double that of filter 66. The carrier frequency at terminals BB is 9200 cycles,'while the envelope at this'point extends from 7200 cycles to 11,200

cycles.

- The function of the carrier frequency multiplier and filter circuit in suppressing interference and As is apparent from the drawing, the filter passes a band of frequencies from 2600 to 6600 cycles. Fig. 5b shows that the input facsimile signal at terminal XX extends from 300 to 4300 cycles. Fig. 5c shows that the major components present at terminals YY' constitute a detected band from to 2000 cycles, a doubled carrier plus envelope band from 2600 to 6600 cycles, and a quadrupled carrier plus envelope band from 7300'to 11,200 cycles. As indicated in Fig. d, the output signals at terminals ZZ are constituted by the double carrier plus envelope band extending from 2600 to 6600.

The above discussion has had reference to marking periods during which a facsimile signal is applied to terminals XX. In Fig. 5e there is shown a noise or interference voltage band extending from zero to 1500 cycles. During spacing intervals no facsimile signal is present in the receiver so these noise or interference voltages will not be modulated on the facsimile carrier. The major portion of the pow-er from interfering voice signals and from ignition noise falls in the band from zero to 1500 cycles, so any suppression which can be produced in this band will greatly lessen the copy sheet background marking. From Fig. 5 it can be seen that at terminals YY the undesired voltages occupy a doubled band extending from zero to 3000 cycles. 'As indicated in Fig.

59, the filter action suppresses the undesired volt ages except those within the narrow band of 2600 to 3000 cycles.

If the undesired voltages are again doubled in frequency, as by adding additional double-filter sections 01 and '68, the undesired voltages at terminals AA will lie outside the pass band of filter 68, so that there will be substantially none of the original undesired voltages present at terminals BB. Of course, some undesired voltages will be present at terminals BB because some of the noise and interference signals will lie above 1500 cycles and because some of the undesired voltages will be quadrupled in frequency by doubler 65 and will pass through filter 00. However,

the power of the undesired voltages at terminals BB of Fig. 4 or terminals ZZ' of Fig. 3 will be sufiiciently low so that marking of the copy sheet background will be substantially reduced.

Suppression of noise and interference signals in the circuit of Fig. 3 is also illustrated in Fig. 6 which is a plot of noise voltage versus frequency. Curve a represents automotive ignition noise present at terminals XX. Curve b shows the noise voltages at terminals YY, while curve 0 shows the substantially reduced noise voltages present at output terminals ZZ.

Fig. 7 shows one recording circuit for copy sheet 48. Copy sheet 48 may comprise a nonelectrolytic conducting paper having-an electrosensitive marking coating thereon and may be of 1 the nature disclosed in U. S. Patents Nos. 2,251,-

742 and 2,528,005, issued August 5, 1941, and October 31, 1950, respectively, to B. L. Kline. This sheet, which may be represented as a variable re sistance element, is connected in series with a resistance 10, the facsimile signals V being applied across the series combination. Y cr 1 6. -In Fig. 8, copy sheet 48 is included in the anode circuit of a tube H. A pair of resistance elements 12 and 13 are coupled in series across copy sheet 48, the facsimile signal V being applied between grid 14 and the junction of resistors 12 and 13. Cathode is connected to ground, while anode 16 is connected to the junction of resistor '12 and copy sheet 48.

Fig. 9, which illustrates the current-shade characteristic of a typical copy sheet material for a given stylus pressure, indicates that the shade is proportional to current through the copy sheet over most of the recording range. However, at a given low value of current, no mark will be recorded on the copy sheet. This constitutes the threshold shade of the copy sheet. At high values of current, shade ceases to vary with current. This constitutes the black shade of the copy sheet. It is evident that noise or interference voltage applied to the copy sheet during spacing intervals need only produce the threshold current through the copy sheet in order to produce an objectionable mark thereon.

The voltage range required to traverse the shade producing current range of Fig. 9 is shown in Fig. 10, which is a plot of current through the copy sheet versus signal voltage. Curve d, which represents the copy sheet alone, indicates that the impedance of the copy sheet decreases from a relatively high value at low signal voltages to a relatively low value at high signal voltages. Using a typical copy sheet, the impedance measured at volts was 27,000 ohms, While the impedance at volts was 3,600 ohms. Because of the variable impedance characteristic of the copy sheet, the voltage range required to cover the entire contrast range may be modified by modifying the circuit in which the copy sheets constitutes a circuit element.

The voltage range M of Fig. 10 represents the voltage variation necessary to cover the contrast range of curve d. The voltage range M, with a typical copy sheet, might be in the order of 4 db, or a facsimile carrier percentage modulation of 37%. If a resistance element in the order of 10,000 ohms is connected in series with the copy sheet, as in Fig. 7, the resulting current voltage characteristic is that of curve e. The voltage range now required to cover the entire contrast range is materially increased, for instance, from 4 db to 14 db.

If the copy sheet is included in the anode circuit of an electron discharge tube provided with negative feedback, as in the circuit of Fig. 8, the voltage range required to cover the entire contrast range decreases to about 8 db. Curve j represents the copy sheet included in the circuit of Fig. 8. The voltage scale of curve 1 differs from that of curves d and e in that it represents grid voltage. When the copy sheet is included in a circuit similar to that of Fig. 8, the ratio of the voltage required to cause a threshold marking current to the total contrast voltage range is increased relatively to the same ratio for the copy sheet alone, as in curve (1, or in series with a resistor, as in curve e. Since an interference or noise voltage must be higher than the threshold voltage to produce a mark on the back ground, a circuit whichincreases this threshold voltage and which also permits use of a high percentage modulation provides a material reduction in background marking.

A comparison of the circuits of Figs. 7 and 8 with respect to these characteristics is given in Figzl-l, which is a-plot of shade brightness versus.

signal. vo ta e in memento oi. signal voltage :im' full black. Cur-very represents atheicgpy :sheetdn. series with a resistor, iwhichumayqbegthe circuit of. Fig. 17' or the copysheet-included- .inthe anode circuit of a pentode. 'Lhe.:.contrast of ;curve. g. varies linearly from black hto-tlzievthreshold shade. Below the threshold-shade. .there .is aqsudden change in contrast to the backgItQund-H-shadel The threshold occurs at approximately 5.2 of full black voltage, and interference orznoisereltages below this level lwillsnot besneqordedsinz the absence .oia carrier si na r mdur ne spacing intervals.

Curve it represents the (circuitcharacteristics; when negative feedback is employed in then-re:- cording amplifier, .as in: Rig. 18. The-threshold level has now .been raised ..to .approximately fi%,. so thatmore than twice the interference; ornoise level can be tolerated during;- spacing intervals. This represents an improvement of ahontfigdh and has been achieved by shortening; and. straightening the recording .characteristiqgof the copy sheet circuit.

The threshold level of the copysheetmanbe increased further by adding'asmalhnegativezbiasr to the rectifiers of ,the,carrier fIQQ-UQHCYLQOHbI BI', as shown in Fig. 12 whereas biaebatterM-Mais shown connected between .doubler rand-terminal Y. Fig. 13 illustrates the transmission loss characteristics ofzdoubler-iii'a for two'flvames:

of .bias voltage. Curve ,i representszero bias,v while curve a representsa small negative bias. such as 1'.5 volts. Making the bias voltage adjustable provides a, eonvenientmeansgof vary.- ing the recording .charaeteristicsecured by :using negative .feedback instherecordingr mplifier.

In .a preferred .embqdiment .of the. .invention using a single .carrierzfrequency doubler-filter stage, a recording amplifier oithentype shown infiglfllandlaidonbler' biasyoltage oi: "-12.5 volts, 2;;

a clear backgmundewas.reecrdedaonlazcopvsheet; in the preseneeioi interferenceza th sontnuhofg the ra io? receiver :havine 'a., peale value :enuali to. 65%..of the,zf-ullhlackasignalilevel. This advan tage was .a chieved,,inmarthhy shortenineaand.

sl'llaightening {the tvoltaeencurrent; recordin characteristic. an impart; y supntessinexmtem ferenoe voltages,

In -..order faithfully- .to; reproduce: the; transmitted. .copy and to achi ve :fnllzaadlvantage n: noise suppression, itis desirable thatxthemfao simile. transmitter have a thresholdlzsimila'r to that of, the receiver; that the: hack? gro nd-pno uces-nocarri r ou pnt,-.and-.-the;-iiehte t s et e iredto.be;recorded deliversmnm xi mately 56% of zthfii black; level.

Figs. 14 and: 15,, which illustrate; a.horrroiete receiver circuit-arrang ment in ccordancemvith,

the invention correspond generally to; the carrangementshowm in Big. 2;

Facsimile-signals; intercepted by .an antenna-4n.

are demodulatedlin EM receiver 4=,l..ansi=.aprilied to filter. 4-2. .ItI-is tQ;1bB understood; that :theiine ventionH-isequally applicable; tooominnnicatinn svstemsothen treguency modulation.

Elle output of filter. 42- is;app1ied-:to;.-carrierfreguenoy doubler, 43. which scomhr-ises rectifiers 9,0, .91.. 8.2:and Bippled. as. indicatedlinvthe-draw mg, .to. provide fullewavev zrectifiea ticnl fllhe:

unction- .of. rectiners .30 and :52- isecennectedsto groun while: the iunstionoi rectiflersiel andz' ae: is connected to one endwimresastonflk. Resist. tor 194;. ispart at amresistance padrmtencouphng doublerrA3z=andrfilters4ucand .comprisingr resistors.

9 5, 95;;311 nd isaz-lconpiediitozothentoi z throughaqeapaeitorztllfi; The tapping of-pot'en tiometer: l.fl5 :is oonnectedu through a conductor 1.011 .to oneqend ofaprimary-winding H18 ofkaen input transformer; J08. 'llhelow-side 10f poten tiometerwi lSzCDIlIlBGfiEd' to the otherend' of'pri mai y winding ilfltifthrougha conductor 4111-.

The secondary winding of transformer l fiil is splitaintortwo halves Hi and .1312; opposite-ends off he respective halvesibeingvcoupled to :oontrol g1- dS'fHfi and H respectively; of -amplifiertubes Htlsand: iii 6 in push-pull .rel'ationship. On end of .eaclr of cathodes slit and '1 I31 are connected together andtoground. 'Iheiother' ends of 'cath' odes Hi and tie ;are.:connected' together and t a. source of; heating-scurrent; ESIIDDJJGSSOI' gIiQS are and tea are iconneoted' together and toground. Screen grids. .llizluand, 2| 221are:connected' together" and coupled"tos'groundithrough the par allel combination of ;a..'zcapaeitori-flflaand aresister 512,43. Screen: grids 112:1 sand 1:2 Z'are'al'smcon nectedato a source of :positive-.;potentia3l through' avoltage e tcrwtube L25 and-aresistor i 26. lnclusioniof. a voltage regulator tube inithe-screen grid supp-1y circuit. preventsamplifien .atubes. 4 t5: and MS from :sirawing': curremituntil the. voltage supply exceeds a predetermined value. if asdynamotor isvused'asrausource ofi hig'h voltage; the: dynamotor willgnot ahe damagedtby undue current drainrbefone it reaches operating speed;

Anodes H25! and I'd-5i cf'tubes *ich5-2and- .l;l;6, respectively, are interooupled .by-va series circuitincluding :a-capaeitor ms, resistors 138-, 13:15, 1232' and {3e ands, capacitor tell. The junctionnof" resistors fill-and ill-i and the junction of resistetors 1.32. and i153 are coupled to controlgrifis 111 3 and, l M, .respeatively, through secondary. wind ing halves LH and l (2, respectively: These' connections provide voltage negative feedback foreach of amplifier tubes -i fi -and H8. The Junetion of resistors 13% and F32 is-connected-"toasource of negative potential thereby to provideandiwillithexzeforesnothe setiorth-gimdetail-l when; the receiver is, tohezused %in La .amqbile installation where*pawerzconsumntionjbecomes;a. sigIIifiQanhfactQr; the amplifier :tuhes may advan taeeousl berealizedi as :type i5m 8.;and the volt,-

age regulator tubes ias tyne flw; Ether could, of course, be used and the voltage regulator tubes might be dispensed with.

g The amplified output signal of tubes I40 and MI is applied to the primary winding of an output transformer I42, the secondary winding of which is coupled tostylus 41. Stylus 41 is caused to scan copy sheet 45 by means of a stylus motor I43. Copy sheet 48 is mounted on a conductive surface of drum 49 which is rotated by motor 50. The surface of drum 49 is connected to ground through normally open contacts I44 of a relay I45. Relay I45, which may be, for instance, a half nut solenoid, is energized through conductors ME and I 41 connected to a control circuit I48. I g a Control circuit I48, which is connected to the output of filter 42 through conductor I49 and I50, is fully disclosed in th copending U. S patent application of C. Jelinek, Ser. No. 230,123, filed June 6, 1951.

Control circuit I48 is also coupled, through conductors II and I52, to a phasing control I53 which is mechanically coupled to motor 50 and which serves properly to phase th rotation of drum 49 in accordance with the received facsimile signal. Phasing control I53, including the mechanical coupling to drum 49, is fully disclosed in the copending U. S. patent application of Frederick G. Hallden et al., Ser. No. 6,846, filed February 7, 1948.

Stylu motor I43 is driven by a frequency generator 154 connected thereto through conductors I55 and I56. Frequency generator I54, which may be of any desired type that will produce a substantially constant frequency, is caused to deliver a driving voltage for motor I 43 under control of control circuit I48.

While the invention has been described in shecific embodiments thereof and in specific uses, it is not desired that it be limited thereto for obvious modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as .set forth in the appended claims.

What is claimed is: g

1. A receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising .a modulated facsimile carrier, a first carrier frequency doubler coupled to said demodulation means thereby to double the carrier frequency of said facsimile signal, means to prevent operation of said carrier frequency doubler for signal voltage levels below a predetermined value, first filter means coupled to said first carrier frequency doubler to suppress transmission of frequencies lying outside the range of the doubled facsimile carrier frequency and its associated modulation envelope, a second carrier frequency doubler coupled to the output of said first filter means to thereby quadruple the carrier frequency of said facsimile signal, second filter means coupled to said second carrier frequency doubler to suppress transmission of frequencies lying outside .the range of the quadrupled facsimile carrier frequency and its associated modulation envelope said facsimile recorder comprising an electric stylus arranged to scan a "copy sheet having a given voltage-current recording characteristic, a recording amplifier having an input circuit con- 10 pled to said second filter means and an output circuit coupled to said stylus, and circuit means intercoupling said output circuit and said input circuit in degenerative relationship at the frequency of said multipled carrier thereby substantially to straighten and shorten the effective re-- cording characteristic of said copy sheet. 7

2. A receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, comprising means to demodulat a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, a first carrier frequency doubler coupled to said demodulation means thereby to double the carrier frequency of said facsimile signaL-first filter means coupled to said first carrier frequency doubler to suppress transmission of frequencies lying outside the rang of the doubled facsimile carrier frequency and its associated modulation envelope, a second carrier frequency doubler coupled to the output of said first filter means to thereby quadruple the carrier nequency of said facsimile signal, second filter means coupled to said second carrier frequency doubler to suppress transmission of frequencies lying outside the range of thequadrupled facsimile carrier frequency and its associated rno'dulation envelope said facsimile recorder comprising an electric stylus arranged to scan a 'c'o'p'y sheet having a given voltage-current recording characteristic, a recording amplifier having an input circuit coupled to said second filter means and an output circuit coupled to said stylus, and circuit means intercoupling said output circuit and said input circuit in -degenerative relationship at the frequency of said quadrupled carrier thereby substantially to straighten and shorten the effective recording characteristic of said copy sheet.

3. A receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, comprising means to demo'dulate a received radio wave having "a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, a carrier frequency doubler comprising a full wave rectifier circuit coupled to said demodulation means thereby to double the carrier frequency of said facsimile signal, means to prevent operation of said carrier frequency doubler for signal voltage levels below a predetermined value, filter means coupled to said carrier frequency multiplier to suppress transmission of frequencies lying outside the range of the doubled fac simile carrier frequency and its associated modulation envelope, said facsimile recorder comprising an electric stylus aranged to scan a copy sheet having a given voltage-current recording characteristic, a recording amplifier having an input circuit coupled to said filter means and an output circuit coupled to said stylus, and circuit means intercoupling said output circuit and said input circuit in degenerative relationship at the frequency of said doubled carrier thereby substantially to straighten and shorten the effective recording characteristic of said copy sheet.

4. .A receiver circuit arrangement for energiiz= ing a facsimil recorder during marking inter vals of a facsimile signal and for suppressing energization of said recorder during spacing in- 11 tervals of said signal, comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, a carrier frequency multiplier comprising a full wave rectifier circuit coupled to said demodulation means thereby to multiply the carrier frequency of said facsimile signal, biasing means coupled to said rectifier circuit to prevent operation of said carrier frequency multiplier for signal voltage levels below a predetermined value, band pass filter means coupled to .said carrier frequency multiplier to suppress transmission of frequencies lying outside the range of the multiplied facsimile carrier frequency and its associated modulation envelope, said facsimile recorder comprising an electric stylus arranged to scan a copy sheet having a given recording characteristic, a recording amplifier having an input circuit coupled to said filter means and an output circuit coupled to said stylus, and circuit means intercoupling said output circuit and said input circuit in degenerative relationship at the frequency of said multiplied carrier thereby substantially to straighten and shorten the effective recording characteristic of said copy sheet.

5. In a receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, the combination comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, a first carrier frequency doubler comprising a full wave rectifier circuit coupled to said demodulating means, first band pass filter means coupled to said first carrier frequency doubler to suppress transmission of frequencies lying outside the range of the doubled facsimile carrier frequency and its associated modulation envelope, a second carrier frequency doubler comprising a full wave rectifier circuit coupled to the output of said first band pass filter means to thereby quadruple the carrier frequency of said facsimile signal, second band pass filter means coupled to said second carrier frequency doubler to suppress transmission of frequencies lying outside the range of the quadrupled facsimile carrier frequency and its associated envelope, said facsimile recorder comprising an electric stylus arranged to scan a copy sheet, a degenerative amplifier having an input circuit coupled to said second band pass filter and an output circuit coupled to said stylus.

6. In a receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, the combination comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, carrier frequency multiplier means couplied to said demodulating means, filter means coupled to the output of said carrier frequency multiplier means, said facsimile recorder comprising an electric stylus arranged to scan a copy sheet having a nonlinear voltage-current characteristic, a recording amplifier having an input circuit coupled to said filter means and an output circuit coupled to said stylus, and circuit means .intercoupling said output circuit and iii said input circuit in degenerative relationship at the frequency of said multiplied carrier thereby to substantially straighten and shorten the effective recording characteristic of said copy sheet.

7. In a receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, the combination comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, a first carrier frequency doubler coupled to said demodulating means, a first filter coupled to the output of said first carrier doubler means, a second carrier frequency doubler coupled to the output of said first filter, a second filter coupled to the output of said second carrier frequency doubler, whereby noise signals are suppressed during the spacing intervals of said facsimile signal, and means operatively coupling the output of said second filter to the said facsimile recorder.

S. In a receiver circuit arrangement for energizing a facsimile recorder during marking inter vals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, the combination comprising means to demodulate a received radio wave having a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, 9, first carrier frequency doubler comprising a full Wave rectifier circuit coupled to said demodulating means, first band pass filter means coupled to said first carrier frequency doubler, a second carrier frequency doubler comprising a full wave rectifier circuit coupled to the output of said first band pass filter means, second band pass filter means coupled to said second carrier frequency doubler whereby noise signals are suppressed during the spacing intervals of said facsimile signal, and means operatively coupling the output of said second band pass filter means to the said facsimile recorder.

9. In a receiver circuit arrangement for energizing a facsimile recorder during marking intervals of a facsimile signal and for suppressing energization of said recorder during spacing intervals of said signal, the combination comprising means to demodulate a received radio wave hav-- ing a modulation component comprising said facsimile signal, said facsimile signal comprising a modulated facsimile carrier, filter means coupled to said demodulating means, a recording amplifier, circuit means coupling said filter means to said recording amplifier input, a facsimile recorder comprising an electric stylus arranged to scan a copy sheet having a nonlinear voltagecurrent characteristic, said recording amplifier having an output circuit coupled to said stylus, and circuit means intercoupling said amplifier output circuit and said amplifier input circuit in degenerative relationship.

EDGAR S. GRIMES.

References Cited in the file of this patent UNITED STATES PATENTS Haynes Aug. 14, 1951 

